Thermo-electric cooler

ABSTRACT

One or more piezoelectric devices cool or heat a thermally-conductive basin. The basin is sized, shaped and arranged to receive two or more food serving trays. In a preferred embodiment, the food serving trays are sized, shaped and arranged to provide an air gap between the tray and the thermally-conductive basin so that the tray is cooled by convection and radiation but not conduction.

BACKGROUND

FIG. 1 is a perspective view of a prior art thermoelectric cooler or chiller 1 designed to cool small volumes of condiments, garnishes or dairy products. The chiller uses a piezoelectric Peltier device 3 located in a lower chamber 4 of the chiller 1. The cold side of the piezoelectric device 3 is thermally coupled to the bottom surface 5 of a thin, thermally-conductive food holding tray 6. The food holding tray 6 fits precisely into a thermally conductive basin 11 that lies just outside the tray 6.

FIG. 2 is a cross-sectional diagram of the prior art chiller shown in FIG. 1 taken across section lines 2-2. The piezoelectric device 3 has its cold side attached to a heat sink 8 thermally coupled to the bottom 5 of the food holding tray 6. A hot side heat sink 9 is provided with air cooling fins to facilitate the transfer of heat absorbed from the cold side, away from the thermoelectric device 3 hot side.

A problem with prior art thermoelectric coolers or chillers shown in FIG. 1 and FIG. 2 is that the food holding tray 6 is sized or configured to snugly fit into a only a custom-sized insert basin 11 in order to maximize heat conduction. A second and related problem with the prior art thermoelectric chillers shown in FIG. 1 and FIG. 2 is that they cool a food insert tray exclusively by thermal conduction and since the food holding tray 6 is typically on the order of an eighth inch thick, evenly cooling the tray contents from top to bottom is problematic. A third problem is that they are able to use only one thermally-conductive food serving tray, i.e., the one provided by the manufacturer.

While heat conduction can transfer heat between the food storage tray 6 and the thermoelectric device 3, conductive heat transfer tends to result in an uneven heat absorption through-out the basin 11. Portions of the basin 11 nearest the Peltier device 3 tend be very cold whereas portions of the basin away from the Peltier device tend to be relatively warm, especially when the basin 11 is fitted tightly against a food holding tray filled with relatively warm food products. The reliance on only thermal conduction to transfer heat between the food products and the Peltier refrigeration device tends to create significant temperature gradients between the bottom of the tray 5 and the open top 7. A thermoelectric cooler that would accept industry-standard inserts and which would provide a more uniform temperature through-out a food holding tray would be an improvement over the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art thermoelectric cooler;

FIG. 2 is a cross section of the prior art thermoelectric cooler shown in FIG. 1;

FIG. 3 is a perspective view of a thermoelectric view that shows the construction of the cooler;

FIG. 4 is a left-side view of a thermoelectric cooler having air gaps between the sides and bottom of a food holding tray and a temperature controlled basin;

FIG. 5 is a front view of the thermoelectric cooler shown in FIG. 3; and

FIG. 6 is a perspective view of the thermoelectric cooler showing a variable speed blower and duct to route room air over the hot-side heat sink of the thermoelectric device.

DETAILED DESCRIPTION

FIG. 3 is a perspective view of a temperature-controlled food storage unit 10. The food storage unit 10 is comprised of a cabinet 12, which supports, encloses and insulates a thermally-conductive basin 14 for storing food products and/or thermally-conductive food serving trays. The basin 14 has an open top 16, four thermally-conductive orthogonal sides 18 and a thermally-conductive bottom 20. A planar top 21 around the periphery of the cabinet 12 supports a thermally-conductive food storage container or tray 36, which hangs into the open volume of the thermally-conductive basin 14 from the planar top surface 21. A refrigeration unit 24 is thermally coupled to the bottom 20 of the basin 14.

FIG. 4 is a side view of the temperature-controlled food storage unit 10 through section lines 4-4. The food storage tray 36 shown in FIG. 4 has an open top 38, sloping or tapered sides 40 that imbue the food storage tray 36 with the shape of an inverted truncated pyramid with a planar bottom 42. Since the sidewalls 18 of the basin 14 are orthogonal to the planar, and horizontal basin bottom 20, the tapered sides 40 of the food storage tray 36 create a generally pyramid-shaped air gap 44 between the sides 40 and the sidewalls 18 of the basin.

The length of the sidewalls 18 determines the location of the bottom of the tray 42 above the bottom of the basin 20. The sidewall length thus effectively determines the space between the basin bottom 20 and the tray bottom 42. The open space between the tray bottom 42 and the basin bottom 20 defines a second, substantially rectangular air gap 46.

The air gap 44 and the air gap 46 allow air currents to exist between the sidewalls and bottom of the food storage try 36 and the side walls and bottom of the basin 14. The air gaps thus allow heat transfer by convection currents.

The air gaps also allow heat to be radiated from warm surfaces to cold surfaces. The air gaps thus allow heat transfer by radiation. Except for very small amounts of heat transfer that can take place between the top edges of the food storage tray 36, which rest on the top surface 21 of the cabinet 12, heat transfer between the food storage tray 36 and the basin 14 is by convection and radiation but not by conduction. Transferring heat by convection and radiation but not conduction is believed to provide a more uniform heat dissipation from the food storage tray 36, which yields a more uniform temperature gradient inside the tray 36.

Refrigerating the basin 14 can be accomplished by having the lower surface 22 of the bottom 20 of the basin 14 thermally connected to a cold side heat sink 26, below which is a solid state heat pump or Peltier device. Peltier devices and their operation are well known to those of ordinary skill in the art. A description of their characteristics and operation is omitted for brevity, they are however considered herein to be solid-state heat pumps.

Air is preferably blown across a finned, hot-side heat sink 28 that dissipates heat from the hot side of a Peltier device. Dissipating heat from the hot side decreases the Peltier device cold side temperature. As the Peltier device cold side gets colder, the temperature of the metal surrounding the cold side of the Peltier device drops, allowing the colder metal to absorb heat.

Temperature sensors 49 are coupled to the lower surface 22 of the basin to provide an electrically measurable representation of the temperature of the basin 14, to a controller or central processing unit 32. The controller or CPU 32 reads the sensors 49 and in response thereto, it modulates the electric power provided to the Peltier device to keep the measured temperature within a preferred operating range.

In one embodiment, the controller/CPU 32 measures a voltage across a temperature-dependent transistor. In another embodiment, the controller/CPU reads the electrical resistance of a thermistor. The temperatures of the sensors 49 thus indicate a temperature of at least the lower surface of the basin 22. By adjusting the power provided to the Peltier device, the temperature inside the basin can be effectively controlled.

FIG. 5 is a cross-sectional diagram of the temperature-controlled food storage unit 10 taken from in front of the unit. FIG. 5 shows two, side-by-side food storage trays 36 suspended in the cabinet 12. The container 36 on the left is depicted as being wider than the container on the right 36 to demonstrate that the temperature controlled food storage unit 10 can be operated with multiple trays 36, as well as trays 36 of different sizes and/or shapes.

In FIG. 5, both trays 36 have open tops 38 and tapered sides 40. Both trays 36 have planar bottoms 42 located above the bottom 20 of the thermally conductive basin 14 to define a lower air gap 46. As stated above, the air gaps 44 and 46 surround both food storage containers 36. FIG. 5 also shows the use and location of a second thermoelectric device 24, which is not visible in FIG. 4 because the second device is located directly behind the first device when the unit 10 is view from either side.

The second thermoelectric device 24 is provided with its own controller 32A and its own temperature sensors 49. The tandem thermoelectric devices 24 in a single basin 14 enable the temperature-controlled food storage unit 10 to sink more from the right side of the basin 14 than from the left side. Using a second Peltier device also allows more heat to be removed from the basin 14 than would otherwise be possible with a single device.

FIG. 5 also shows the hinged thermally insulated covers 48 for both trays and shows that the covers 48 are in their closed positions. The thermally insulated covers 48 significantly improve the thermal efficiency of the food storage unit 10 due to the fact that convection currents in a room where the unit is used will tend to heat the interior volume and the contents of the two trays 36.

FIG. 6 shows a perspective view of the bottom portion of the cabinet 12 and an optional variable speed blower 52 that forces room air through a duct 54 that routes room air through and around cooling fins formed as part of the hot side heat sink 28. Those of ordinary skill in the art will recognize that an increased air flow provided by the variable speed blower 52 enables the hot side of the Peltier device 24 to dissipate more heat than would otherwise be possible. The increased heat dissipation from the hot side decreases the cold side temperature which enables the cold side heat sink 26 to absorb more heat from the thermally conductive basin 14.

In a preferred embodiment, the fan speed and/or Peltier device 24 power is modulated by the controller/CPU responsive to the temperature of the thermally conductive basin 14, as measured by one or more of the temperature sensors 49. If the temperature inside the basin 14 falls below a predetermined value, the blower speed is reduced and/or the power to the thermoelectric device 24 is adjusted to keep the temperature of the basin 14 within desired limits.

As stated above, a problem with prior art thermoelectric chillers is their exclusive reliance on conductive heat transfer between a thermoelectric device and a food product to be cooled. In the embodiments shown in FIGS. 3-6, one or more air gaps 44 between the sides of the food storage containers 36 and the basin 14 permit heat energy to be transferred from the basin by radiation as well as convection because the air gaps 44 allow convection currents to exist in the cooler 10 and to transfer heat away from the food storage tray 36. Stated another way, the embodiment shown in FIGS. 3-6 allow heat to be transferred from the food storage basin 36 to the conductive basin 14 by radiation, and convection. In an alternate embodiment, the bottom of the tray 42 can be located adjacent to and in thermal contact with the bottom of the basin 20 to facilitate heat transfer by conduction as well.

In a preferred embodiment, the conductive basin 14 is sized, shaped and arranged to receive two or more industry-standard food storage containers 36 and to provide the aforementioned one or more air gaps around the exterior of a food storage container 36. The cabinet 12 is preferably provided with separate and independently hinged thermally insulated covers 48 for each basin 36. In another embodiment, the food storage containers 36 in the basin are configured to receive a thermal insert as described in the U.S. patent application Ser. No. 12/329,795, the contents of which are incorporated herein by reference as well as a thermal insert described in U.S. patent application Ser. No. 12/478,439, the contents of which are also incorporated herein by reference.

While the preferred embodiment of the food storage unit 10 is of a cold storage unit, those of ordinary skill in the art will recognize that the food storage unit 10 can also be a hot food storage unit by simply reversing the orientation of the Peltier device. And while the preferred embodiment uses a Peltier device as a refrigeration unit to refrigerate the basin 14, alternate embodiments use ice, cold water, an ice/water slurry and a conventional compressed gas refrigeration units. Alternate embodiments of a hot food storage unit steam, hot water and electrically-resistive heaters thermally coupled to the basin 14.

The foregoing description is for purposes of illustration only. The scope of the invention is defined by the appurtenant claims. 

1. A temperature controlled food storage unit (food storage unit) comprised of: a cabinet; a thermally conductive basin (basin) within the cabinet, the basin having an open top, four sides and a bottom; a refrigeration unit within the cabinet having a first side thermally coupled to the basin and having at least one second side thermally coupled to a heat sink, the basin being configured to receive a thermally conductive food storage container (container) comprised of an open top, at least first and second sides and a bottom, the container being sized, shaped and arranged to be suspended in the basin from at least one of the cabinet and the basin, and being sized, shaped and arranged to provide an air gap between a side of the container and a side of the basin.
 2. The food storage unit of claim 1, wherein the refrigeration unit is a Peltier device.
 3. The food storage unit of claim 2, further including an air gap between the bottom of the basin and the bottom of the container.
 4. The food storage unit of claim 1, wherein the air gap between sides of the container and sides of the basin, is configured to transfer heat convectively between the basin and the container through air in the air gap.
 5. The food storage unit of claim 2, wherein the air gap between sides of the container and sides of the basin, is configured to transfer heat convectively between the basin and the container through air in the air gap.
 6. The food storage unit of claim 1, wherein air gaps between the basin and container are configured to allow heat transfer between the basin and container via air convection currents and infrared radiation but not via conduction.
 7. The food storage unit of claim 5, wherein the air gaps between basin and container are configured to allow heat transfer between the basin and container via air convection currents and infrared radiation but not via conduction.
 8. The food storage unit of claim 1, wherein the container sides are tapered inwardly from the open top of the container to the bottom of the container.
 9. The food storage unit of claim 1, 6, 7 or 8, further comprised of a thermally-insulated cover for the container, the thermally-insulated cover being hingedly attached to at least of the cabinet and the basin to rotate around a hinge between open and closed positions.
 10. The food storage unit of claim 1 or 2, further comprised of a plurality of containers in said basin and a corresponding number of thermally-insulated covers, each thermally-insulated cover being hingedly attached to at least of the cabinet and the basin to rotate around a hinge between open and closed positions for each container.
 11. The food storage unit of claim 1 or 2, further comprised of temperature sensor, thermally coupled to the basin, the temperature sensor effectuating temperature control of the basin.
 12. The food storage unit of claim 11, wherein the temperature sensor is a thermistor.
 13. The food storage unit of claim 11, wherein the temperature sensor is a transistor.
 14. The food storage unit of claim 11, wherein the temperature sensor acts to control the electric power applied to the refrigeration unit.
 15. The food storage unit of claim 11 wherein the temperature sensor acts to control air flow across the heat sink. 